1. Field of the Invention
The present invention relates to a rechargeable battery, and more particularly, to a rechargeable battery with an integrated protection circuit having high rigidity to withstand an external impact.
2. Description of the Related Art
Generally, batteries are divided into two groups: general batteries, which are non-recoverable once used and rechargeable batteries, which are recoverable. Rechargeable batteries are chemical cells capable of charging and discharging and are widely used as small-scale batteries for small-scale devices such as portable phones and notebook computers as well as large-scale batteries such as industrial power storage batteries and batteries for use in electric motor cars.
Currently used batteries such as lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and lithium-ion batteries have recently garnered attention due to a sharp increase in demand for portable electronic devices. Particularly, lithium ion batteries have become popular because they have a high energy density and high operating voltage, excellent conservation and life properties and are environmentally friendly.
In order to protect rechargeable batteries, a protection circuit is necessary. For example, if a voltage of the battery exceeds a specific value, the protection circuit stops the charging of the battery to prevent overheating or explosion due to overcharging. Furthermore, if a voltage of the battery is less than a specific value, the protection circuit can stop the discharging of the battery to prevent battery damage due to over-discharging. The protection circuit can also stop the discharging of the battery if an abnormal current flow exists in the battery due to an instrumental error. The protection circuit may also instantaneously stop the charging of the battery if a dangerously large amount of current flows in the battery due to an external short-circuiting of a battery pack. Thus, rechargeable batteries integrated with such a protection circuit are currently being used.
FIG. 1 is a perspective view of a related art rechargeable battery with an integrated protection circuit. FIG. 2 is a perspective view of a related art rechargeable battery with an integrated protection circuit in which a molding member has been removed. FIG. 3 is a vertical sectional view of a related art rechargeable battery with an integrated protection circuit as shown in FIG. 1.
Referring to FIGS. 1 and 3, the related art rechargeable battery with an integrated protection circuit comprises a case 10 having an enclosed internal space for housing a battery cell 12, a circuit board 30 having a protection circuit electrically connected to a plane of the case 10, and a molding member 32 injection molded on a plane of the case 10 for covering the circuit board 30.
The case 10 comprises a receptacle member 9 having an opening, a battery cell 12 installed in the receptacle member 9, and a cover member 16 enclosing the opening of the receptacle member 9 to prevent the flow of electrolyte out of the receptacle member 9. Preferably, the cover member 16 is joined to the receptacle member 9 by laser welding to enclose the opening of the receptacle member 9. The receptacle member 9 and the cover member 16 may be made of aluminum or stainless steel.
The circuit board 30 having the protection circuit is electrically connected to the cover member 16 of the case 10 through a connecting member 25. Furthermore, as shown in FIG. 3, the molding member 32 is injection molded to the cover member 16 of the case 10 so that a terminal 31 of the circuit board 30 is exposed to the outside. The molding member 32 is made of a nylon-type resin and injection molded under a low temperature and low pressure to protect the circuit board 30 having the protection circuit.
The connecting member 25 is made of nickel having good conductivity and is formed as a plate having a thickness of 0.2 mm. Using spot welding, an end of the connecting member 25 is connected to the circuit board 30 while another end thereof is connected to the cover member 16 of the case 10. Referring to FIG. 4, in an attempt to more firmly bond and couple the molding member 32 to the case 10, the molding member 32 is injection molded to cover a predetermined portion of the outer periphery of the cover member 16.
However, when the molding member is injection molded to the cover member of the battery body, the battery body and the molding member are not firmly bonded to each other. Therefore, the related art rechargeable battery with integrated protection circuit is problematic because the spot welding portion of the connecting member may sever if the battery is dropped, receives an external impact, or cracks, thus degrading the power source.
Additionally, when the molding member is injection molded to cover the outer periphery of the cover member of the battery body, because the thickness of the molding member bonding to the outer periphery is no more than 0.2 mm, the molding member lacks the strength to uphold the bond. Over time, a gap is generated between the battery body and the molding member. Accordingly, the battery may produce air bubbles. This is a problem when labeling the surface of the battery, as the air bubbles increase the overall thickness of the labeled battery.